Too Much Food or Too Little Movement?

What does it mean that the world has such an excess of obesity? Is it the consequence of too much food? The wrong kind of food? Too little movement? These questions have no definitive answers. But one more analysis this week attempts to answer them anyway.

Published in the American Journal of Medicine, this study examined data from the National Health and Nutrition Examination Survey (NHANES) on obesity, physical activity, and food intake. They found that self-reported caloric intake did not change between 1988 and 2010. But they found a substantial increase in the number of both men and women who reported no leisure-time physical activity. And they found a correlation between the trends they observed in physical activity and the rising prevalence of obesity.

This was all the news media needed to start writing provocative headlines like:

You’re Obese Because You’re Lazy, Not Because You Eat Too Much

But such conclusions are not scientifically valid. That’s because self-reported diet and exercise data — even from NHANES — is about as solid as jelly. People shade the truth when they report exercise and eating behavior. And how much they fib changes with the circumstances in ways that are virtually unknowable.

That’s why experts have repeatedly published warnings about this problem. “Self-report–based estimates of energy intake offer an inadequate basis for scientific conclusions” is the title of one recent paper that explains it well.

So we are left with competing mythologies about why we have an excess of obesity. People can pick the version that suits their purpose. But remember none of these versions are definitively known to be true. Perhaps what matters more is an evidence-based approach to reversing the trend and reducing the burden of disease.

“Myths are stories that express meaning, morality or motivation. Whether they are true or not is irrelevant.” — Michael Shermer

Click here to read more from NPR, here to read the study in the American Journal of Medicine, and here to read more about the problems with self-reported dietary data.

Eat, photograph © Thomas Hawk / flickr

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